How can you determine the moisture content of a concrete block (CMU) wall, and how can you judge when the moisture level is sufficiently low to paint?

From
Zenith Czora of Crommelin on
January 11, 2018:Using a moisture meter like Tramex CME4, depending on the moisture content, the measurements are made to a depth of several centimeters. The concrete wall is deemed dry enough to coat when the moisture content is not more than 5.5 percent. The other type of moisture meter is Radio Frequency Moisture Meter, where the detection of moisture is displayed on a relative scale from dry to damp, rather than by percent moisture. If there is no moisture meter available, the plastic sheet method is the way to go.This method is a qualitative test and does not really measure moisture content but shows evidence of moisture and whether the moisture is moving toward the wall, in which case the CMU wall is typically ready for coating application. This test involves covering the surface of the CMU wall with impermeable material such as plastic sheet. A 460X460-mm square of 0.1-mm thick plastic
sheet is placed on the CMU wall surface and sealed around the edges with tape. After 16 to 24 hours, the sheet is removed and the area
is inspected for moisture or color darkening. Color darkening occurs in some instances when the moisture movement is slow and there is still a slight dampness on the surface.Please read the article, MOISTURE IN CMUs: WHEN IS IT SAFE TO PAINT, from D+D, Spring, 2017